Following Vytautas’s death in 1430, Lithuania entered another civil war as rival factions competed for power. Despite moments of tension, the Jagiellonian dynasty, founded by Jogaila, ensured that Lithuania and Poland remained connected under shared leadership from 1386 to 1572. Although Lithuanian nobles at times broke the union by selecting grand dukes independently—such as in 1440, when Casimir, Jogaila’s second son, was named Grand Duke—the situation was repeatedly resolved when these leaders were later elected kings of Poland. This pattern of dynastic cooperation benefited both realms, ensuring political continuity and protection against external threats.
Rising Threats and Regional Conflicts
The Teutonic threat diminished after the Peace of Thorn in 1466, which saw much of Poland’s lost Piast territories recovered. However, new dangers emerged, particularly from the Crimean Tatars, who began raiding Lithuanian lands in search of slaves and wealth. In 1482, the Tatars burned Kyiv, and by 1505, they advanced as far as Vilnius, forcing Lithuania to relinquish many of its southern Black Sea territories by the late 15th century.
Meanwhile, the rise of the Grand Duchy of Moscow posed an even more serious challenge. Beginning in 1492, Ivan III of Russia launched the first in a series of Muscovite–Lithuanian Wars, with Moscow aiming to reclaim former Orthodox territories. As a result, Lithuania lost one-third of its territory to Russia by 1503, and the loss of Smolensk in 1514 dealt a further blow, despite a subsequent Lithuanian victory at the Battle of Orsha. These conflicts made Poland’s involvement in Lithuania’s defense increasingly necessary, solidifying the importance of their alliance.
Livonian War and Struggles in the North
In the north, Lithuania and Poland competed for control of Livonia, a region critical for both economic and strategic reasons. The Treaty of Pozvol (1557) established an alliance between the Polish-Lithuanian state and the Livonian Confederation, prompting Ivan the Terrible to launch attacks on Livonia and Lithuania. The fall of Polotsk in 1563 marked a serious setback for Lithuania, although it achieved a temporary victory at the Battle of Ula in 1564. Despite military successes, Livonia was divided among Russia, Sweden, and the Polish-Lithuanian side, as the struggle for dominance in the Baltic intensified.
The increasing pressure from Moscow and the Tatars, along with the challenges of the Livonian War, underscored Lithuania’s need for closer cooperation with Poland. The Jagiellonian rulers balanced internal dynastic politics while maintaining Lithuania’s autonomy and preserving the personal union with Poland, ensuring the survival of both realms amidst constant external threats.